Science ( Making use of Electricity (8.6 only) ) Flashcards
All electrical appliances are _____ _____. They convert electrical energy to other _____ of energy
- energy converters
- forms
A hair dryer converts _______ energy to the ______ energy of the fan, the thermal energy given out by the heating coil and the ____ energy given out by different parts of the hair dryer.
- electrical
- kinetic
- sound
True or false
1 Mains electricity is generated in power stations.
2 The mains voltage in Hong Kong is 220 V.
3 The sockets in a home are connected in series.
4 Electricity is supplied to our homes through the live wire and the earth wire.
1T
2T
3F
4F
Which of the following electrical appliences use the heating effect of current?
(1) Toaster
(2) Electric iron
(3) Electric kettle
1 2 and 3
Which of the following electrical appliences use the magnetic effect of current?
(1) Electric fan
(2) Rice cooker
(3) Vacuum cleaner
1 and 3
What is the color of live wire, Neutral wire and Earth wire
Live wire: brown
Neutral wire: Blue
Earth wire: Green and Yellow
Which wire is connected to the fuse?
Live wire
1 When too many electrical appliances are connected to a mains socket, _________ occurs
2 A ______ breaks a circuit when the current becomes too large. It has a metal wire with a low melting point. The number on it is the _______.
overloading
fuse
fuse rating
A ________ _ also cuts off the current when the current becomes too large. We can reset it from the ‘OFF’ mode to the ‘ON’ mode.
Circuit breaker
T or F
1 overloading and short circuits are dangerous and should be avoided.
2 Fuses and circuit breakers reduce the risk of the circuit overheating
3 A suitable fuse should have a rating much higher than the normal operating current of the applience.
4 A fuse can be reset after it blows
5 The live, neutral and earth wires of an appliance all carry a current under normal operations.
1 T
2 T
3 F
4 F
5 F
The fuse rating is usually marked in _______.
ampere
The fuse in a three-pin plug should be connected to ________.
the live wire
A vacuum cleaner normally works with a current of 9A. If a 5A fuse is used, what happens?
The fuse blows and the cleaner cannot operate
What is the use of the earth wire in a three-pin plug?
To protect the user from getting an electric shock.
Which of the following statements about earth wire are correct?
(1) The earth wire connects the metal case of the appliance to the ground.
(2) The current flows to the ground through the earth wire when the live wire touches the metal case accidentally
(3) The earth wire blows when a fault occurs.
1 and` 2
When an electric fans is full of dust, what possible danger is there? (state one) And how can we prevent this?
Short circuit
Clean the fan
When a short circuit occurs, a large ______ flows in the circuit. This may ______ and damage the fan.
Current
overheat
What happens if there too many electrical appliances connected to a single mains socket?
- Too many electircal appliances are connected to a single mains socket
-> Current flowing through the circuit may become very large
-> Overloading may occur
-> Strong heatin effect of the large current may result in a fire
What happens during a short circuit?
- Short circuit
-> WIre provides a path with very low resistance
-> A large current will pass through the wire
-> Large current causes the thin wire to heat up and glow.
-> May overheat and damage an electrical appliance
What is the working principle of the fuse?
*Principle of fuse
-> Current passing through the fuse is larger than the fuse rating
-> Meral wire in the fuse melts and the fuse blows
-> The circuit becomes open
-> Current is cut off to prevent the circuit from overheating
State the function of the earth wire.
- Function of the earth wire
-> If the live wire is damaged and it touches the metal case of an electrical appliance.
-> The circuit is shorted by the earth wire. Current flows to the ground through the
earth wire and blows the fuse.
-> The current from the mains is cut off. This protects us from an electric shock.
